Weight/Strength of aluminum versus plastics

At parity of maximum resistance before failure (in the case of aluminum, deformation), weighs less aluminum or plastic?
Let me explain better: if i apply a force of 1000N on one end of a rectangular plate with a fixed fulcrum on other side, beyond this force both materials deforms / break. The plastic will obviously have a greater thickness of aluminum to counter the force. Now, will weigh more the plate of plastic or aluminum?

There are many different kinds of plastic you'd have to be specific about which one. I suspect there are different ways of preparing aluminum also (heat treating, peening etc.). You need to be more specific.